Extension Dairy Team

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Preparing For Drought Stressed Crops

Posted: August 7, 2005

For many parts of Pennsylvania, drought has plagued crops since spring. It has been at least 2 years since many of us had to contend with drought stressed crops. As harvesting dates grow closer for corn and sorghum, keep in mind some points related to nitrate toxicity.

To reduce nitrate levels in drought-stressed plants, harvest crops in the afternoon on a warm sunny day; be sure to wait 3 to 5 days after an appreciable rain or long cloudy spell. Since nitrates accumulate in the stalks, the crop may be cut somewhat higher above the ground than usual. The typical recommendation is to leave 10 to 12 inches in the field however a lot of corn is very short this year, so an adjustment to this recommendation may be needed. If in doubt, consult with cooperative extension, your crop advisor, or nutritionist.

If high nitrate levels are suspected, use forage as silage rather than green-chop. Ensiling reduces nitrates by 50 to 60 percent. Ideally, allow the forage to ferment for 3 to 4 weeks before feeding to allow the fermentation process to complete.

Any suspect feed should be tested for nitrate levels. The most critical factor influencing possible toxicity is rate of nitrogen intake, which is affected by forage dry matter intake over a given time period. Feeding practices that regulate dry matter intake can be used to manage high nitrate forages. When stored forages contain more than 1,000 ppm NO3-N, intakes generally must be managed to avoid elevated methemoglobin levels in the blood and other toxic effects.

Consumption of high nitrate forages (or high consumption in the total mixed ration including water) affects cattle via nitrate being reduced to nitrite in the rumen. Nitrite, which is absorbed into the bloodstream, combines with hemoglobin to form methemoglobin, which cannot carry oxygen to the tissues. Thus the animal can die from suffocation in situations of acute toxicity. Animal symptoms include muscular rapid breathing, and discoloration of mucous membranes. Vaginal and other mucous membranes may turn from pink to a gray-brown as methemoglobin contents increase.

More information can be found at http://das.psu.edu/ in the publication From Harvest to Feed: Understanding Silage Management. Additional information is available on feeding strategies for high nitrate forages as well as guidelines on the amount of forage to feed in a single meal based on forage NO3-N levels.